linux-kernel - Re: [RFC v4 06/31] richacl: In-memory representation and helper functions

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Date:	Thu, 25 Jun 2015 23:06:20 +0200
From:	Andreas Grünbacher <andreas.gruenbacher@...il.com>
To:	"Stefan (metze) Metzmacher" <metze@...ba.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux FS-devel Mailing List <linux-fsdevel@...r.kernel.org>,
	Linux NFS Mailing List <linux-nfs@...r.kernel.org>,
	Linux API Mailing List <linux-api@...r.kernel.org>,
	samba-technical <samba-technical@...ts.samba.org>,
	linux-security-module@...r.kernel.org
Subject: Re: [RFC v4 06/31] richacl: In-memory representation and helper functions

Hi,

2015-06-25 21:58 GMT+02:00 Stefan (metze) Metzmacher <metze@...ba.org>:
> Is that also the on disk representation?

that's not the xattr representation, no.

> I'm wondering if the size of an ace should be dynamic,
> which might make it possible to support other ace types
> in future. E.g. supporting other identities like 128-bit values
> to make it easier to map Windows SIDS.

I'm working on additionally supporting unmapped user@...ain and
group@...ain identifier strings; we have to deal with that case in the
nfs client; that may be useful for Samba as well.

> Even without 128-bit ids, it would be very useful to mark an
> ace so that it applies to a uid or gid at the same time.
> This would reduce the size of the ace list when Samba uses
> IDMAP_TYPE_BOTH, which means a SID is mapped to a unix id, which
> is user (uid) and group (gid) at the same time. This feature is required
> in order to support SID-Histories on accounts.
> Currently Samba needs to add two aces (one uid and one gid)
> in order to represent one Windows ace.

It's not clear to me if supporting this would be a good idea right now.
The kernel would have to treat each such entry like two separate entries
internally. How would we map a combined user-space "uid + gid"
number to a kernel uid and gid since it could map to two distinct
numbers there?

> I haven't looked at the claims based acls on Windows, but it would be
> good if the new infrastructure is dynamic enough to support something
> like that in a future version.

I don't know, I have yet to see a use case that isn't totally crazy.

Thanks,
Andreas
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